Piston machine, especially fluid piston machine

ABSTRACT

A piston machine, in particular a fluid piston machine, is described as having a plurality of piston units, which have differently sized output volumes for reasons of geometry, and are able to be deactivated individually for the discrete adjustment of a total output volume of the piston machine. In this context, the larger output volume of one of the piston units is twice as high as the next smaller output volume of one of the other piston units.

FIELD OF THE INVENTION

The present invention relates to a piston machine, especially a fluidpiston machine, having a plurality of piston units which, for reasons ofgeometry, have output volumes of different size, and which are able tobe deactivated individually for the discrete adjustment of an overalloutput volume of the piston machine.

BACKGROUND INFORMATION

Piston machines of the type described at the outset are known from therelated art. In many technological fields piston machines are used aspumps and/or motors. Different principles are known for generating avariable volumetric flow or volume flow, possibly also a variablepressure (pump) or rotational speed and torque (motor). Conventionaltypes for the continuous variation/setting of the output volume of thepiston units are, for example, piston machines having a swash plate, anoblique axis or a wobble plate. By changing the angle, the upper andlower dead centers of the piston strokes are varied and the outputvolume continually modified in this manner. However, such constructionshave low efficiency, especially in the partial-load range. This lowefficiency essentially is due to the leakage at the correspondingcontrol, oblique or swash plate, the friction at the control/oblique orswash plate as well as a constantly required control current forsupporting the control/oblique or swash plate. In addition to acontinual variation of the output volume or the delivery time of thepiston units, it is also known to implement discrete variations of theoutput volume by deactivating individual piston units or switching themoff.

European patent document EP 1 306 553 A2 discusses a piston machine inthe form of a fuel pump, in which individual piston units are switchedoff, thereby allowing for a discrete adjustment of the total outputvolume; to provide greater adjustment options, the output volumes of theindividual piston units are of different size.

SUMMARY OF THE INVENTION

The piston machine according to the exemplary embodiments and/orexemplary methods of the present invention has the features describedherein. Accordingly, the piston machine is developed in such a way thatthe larger output volume of one of the piston units is twice as large asthe next smaller output volume of one of the other piston units. That isto say, the piston units have output volumes of different sizes, and thepiston unit having a greater output volume is designed such that itsoutput volume is twice as large as that of the other piston unit havingthe next smaller output volume. For example, when three piston units areprovided, the output volume of the second piston unit is twice as highas that of the first, and the output volume of the third piston unit istwice as high as that of the second piston unit. This appliesanalogously to any other number of piston units of the piston machine.This makes it possible to vary or adjust the total output volume of thepiston machine in discrete manner in equidistant stages.

In the aforementioned exemplary embodiment featuring three piston units,it is possible to adjust eight different total output volumes, from zeroto seven times the output volume of the piston unit having the smallestoutput volume. For practical purposes, the piston units are configuredin such a way that the stage in the increase or reduction of the totaloutput volume in each case corresponds to the output volume of thepiston unit having the smallest output volume. This creates a pistonmachine whose total output volume is variably adjustable in equidistantstages and which provides high efficiency even in partial-load range.

Furthermore, each piston unit is assigned a switchable drain valve fordeactivating the piston unit. The drain valve is designed such thatopening of the drain valve prevents pressure from being generated in thepiston unit, thereby preventing the supply of fluid. The drain valvethus allows the volume contained in the piston unit to “run dry”.

Advantageously, the drain valve furthermore is developed in such a waythat during opening of the drain valve, the exit cross-section of thepiston unit through which the volume to be output is to be pumped issealed simultaneously. As an alternative, the drain valve may also bedeveloped in such a way that it prevents an inflow of fluid into thepiston unit, so that the piston unit is drained. Of course, quitedifferent deactivation mechanisms for the particular piston unit areconceivable as well. For example, each piston unit may be driven by aseparate drive shaft, so that the drive shafts are able to be controlledor switched off individually.

According to one further development of the exemplary embodiments and/orexemplary methods of the present invention, the piston units have abypass channel assigned to the corresponding drain valve. The bypasschannel returns the undesired volume, which was output by the pistonunit nevertheless, past a consumer, so that the volume is resupplied tothe piston machine “in unused condition”.

Furthermore, the piston machine is to have at least three piston units.This already makes it possible, as stated before, to adjust eightdifferent total output volumes of the piston machine in equidistantsteps/stages.

For practical purposes, the piston machine is developed as a radialand/or in-line piston machine. This reduces both friction losses andlosses caused by leakages, and it ensures high efficiency of the pistonmachine, especially in partial-load range.

Each piston unit advantageously has at least one piston which is axiallydisplaceable inside a cylinder. It is also conceivable to provide twocylinders for each piston unit, each having a piston which is axiallydisplaceable therein. In this case, they form a piston set. Accordingly,the total output volume is adjustable by varying the output volume ofthe piston set. Additionally it is conceivable, for example, that onlythe output volume of one of the piston-cylinder units of a piston set isdeactivated. This allows further gradations in the adjustment of thetotal output volume of the piston machine.

For practical purposes, the differently sized output volumes of thepiston units are defined by differently sized cross-sectional areas ofthe cylinders and pistons. This geometric construction easily makes itpossible to provide and ensure the different output volumes, asdescribed earlier.

As an alternative or in addition, the output volumes of different sizesare definable by piston strokes of different magnitude of the pistonunits.

Notwithstanding the fact that previously the function of the pistonmachine was essentially described as that of a piston pump, one skilledin the art naturally understands that the afore-described specificdevelopments are also applicable to piston machines developed as pistonmotor.

In the following text, the exemplary embodiments and/or exemplarymethods of the present invention are elucidated in greater detail withthe aid of an exemplary embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of an advantageous piston pump in aschematic representation.

FIG. 2 shows an adjustable total output volume of the piston pump.

FIG. 3 shows another adjustable total output volume of the piston pump.

FIG. 4 shows another adjustable total output volume of the piston pump.

FIG. 5 shows another adjustable total output volume of the piston pump.

FIG. 6 shows another adjustable total output volume of the piston pump.

FIG. 7 shows another adjustable total output volume of the piston pump.

FIG. 8 shows another adjustable total output volume of the piston pump.

FIG. 9 shows another adjustable total output volume of the piston pump.

DETAILED DESCRIPTION

FIG. 1 constitutes a schematic representation of a piston machine 1 forfluids, which is developed as in-line piston pump 2. For this purpose,piston machine 1 has three cylinders 3, 4 and 5 formed inside a housing,in which a piston 6, 7 and 8 is supported in axially displaceablemanner. Pistons 6, 7, 8 in cylinders 3, 4, 5 are displaced by a drivablecrankshaft 9. Cylinder 3 and piston 6, cylinder 4 and piston 7, as wellas cylinder 5 and piston 8 form a piston unit 10, 11 or 12 of pistonmachine 1 in each case. Piston units 10, 11 and 12 have different outputvolumes, which are defined by the size of the individual cross-sectionalsurfaces of cylinders 3, 4, 5 and pistons 6, 7, 8. In an advantageousmanner, volume v₁₁ of piston unit 11 is twice as large as volume v₁₀ ofpiston unit 10, and volume v₁₂ of piston unit 12 is twice as large asoutput volume v₁₁ of piston unit 11. Thus, the greater output volume ofone of the piston units in each case is twice as large as the nextsmaller output volume of another piston unit.

In general, the output volume of piston units 10, 11, 12 may thus beexpressed as

V _(i)=2·V _(i-1) , i corresponding to the number of piston units.

Each piston unit 10, 11, 12 or each cylinder 3, 4, 5 is assigned a drainvalve 13, 14 and 15, respectively. From each drain valve 13, 14, and 15,the volume supplied by corresponding piston unit 10, 11 or 12 is guidedout of piston machine 1 by a bypass channel 16, 17 and 18 in “unusedcondition”, provided the individual drain valve 13, 14, 15 is switchedappropriately, i.e., is open. For practical purposes, bypass channels16, 17 and 18 are combined to form a common (return) channel, which isnot shown here. By opening drain valves 13, 14 and/or 15, individualpiston unit 10, 11 or 12 is thus able to be switched off, so that theoutput volume it has supplied is not pumped but forwarded unused, orreturned, and therefore not supplied to the total output volume ofpiston machine 1.

By deactivating piston units 10, 11, 12, or setting drain valves 13, 14,15, it is therefore easily possible to vary the total output volumeV_(G) of piston machine 1 in equidistant stages in discrete manner. Thisis best represented by the following formula

$V_{G} = {{\sum\limits_{i = 1}^{n}{\left( {x_{i} \cdot V_{10} \cdot 2^{i - 1}} \right)\mspace{14mu} {with}\mspace{14mu} x_{i}}} \in \left\{ {0;1} \right\}}$and  n ∈ N(n = numberofpistonunits).

Due to the afore-described advantageous development of piston machine 1,the particular abrupt change between the different total output volumescorresponds to the output volume of the piston unit having the smallestoutput volume, in this case, v₁₀. Maximum total output volume V_(G,max)corresponds to:

${V_{G,\max} = {{\sum\limits_{i = 1}^{n}\left( {V_{10} \cdot 2^{i - 1}} \right)} = {V_{10} \cdot \left( {2^{n} - 1} \right)}}},$

in this case,

$V_{G,\max} = {{\sum\limits_{i = 1}^{3}\left( {V_{10} \cdot 2^{i - 1}} \right)} = {{{V_{10} \cdot 2^{0}} + {V_{10} \cdot 2^{1}} + {V_{10} \cdot 2^{2}}} = {7 \cdot V_{10}}}}$

FIGS. 2 through 9 illustrate the output volume of piston units 10, 11,12 and the total output volume of piston machine 1 or in-line pistonpump 2 derived from the corresponding adjustment of drain valves 13, 14and 15. The delivered (dashed line) output volume supplied by individualpiston units 10, 11 and 12, and the possible (blank) output volume ofpiston units 10, 11, and 12 are shown on the left side. Accordingly, theresulting total output volume V_(G) is shown on the left side.

FIG. 2 shows the corresponding output volumes in the event that allbypass channels 16, 17 and 18 are enabled by corresponding drain valve13, 14 and 15 or in case all piston units 10, 11, 12 are deactivated, sothat none of the potential output volumes is utilized and the totaloutput volume V_(G) is equal to zero.

If drain valve 13 is closed, i.e., piston unit 10 is activated, as shownin FIG. 3, then total output volume V_(G) corresponds to the outputvolume of piston unit 10.

According to FIG. 4, piston unit 10 is deactivated and piston unit 11 isactivated, so that the resulting total output volume corresponds to theoutput volume of piston unit 11 and thus to twice the output volume ofpiston unit 10.

If piston unit 10 is switched on as well according to FIG. 5, thenresulting total output volume V_(G) is supplemented by output volume V₁₀of piston unit 10, i.e., increased by an additional stage.

By deactivating piston units 10 and 11 and activating piston unit 12, atotal output volume V_(G)=V₁₂ results, which once again is one stagegreater than the previous output volume.

To increase the total output volume by another stage, piston unit 10 isswitched on as well according to FIG. 7.

To increase the output volume by yet another stage, piston unit 10 isdeactivated and piston unit 11 is activated, according to FIG. 8.

FIG. 9 shows the setting of piston machine 1 or in-line piston pump 2 inthe event that maximum total output volume V_(G,max) is set. All threepiston units 10, 11, 12 are activated for this purpose, i.e., none ofpiston units 10, 11, 12 is deactivated. In this case,V_(G)=V_(G,max)=7·V₁₀.

With the aid of advantageously developed piston machine 1, it istherefore easy to adjust a total output volume V_(G) discretely, inequidistant stages (V₁₀), it already being possible to adjust eightdifferent total output volumes in case of three differently developedpiston units 10, 11, 12, at unchanged high efficiency.

1-8. (canceled)
 9. A piston machine, which is a fluid piston machine,comprising: a plurality of piston units, which have differently sizedoutput volumes for reasons of geometry, and which deactivatableindividually for the discrete adjustment of a total output volume of thepiston machine; wherein a greater output volume of one of the pistonunits is twice as high as a next smaller output volume of one of theother piston units.
 10. The piston machine of claim 9, wherein each ofthe piston units is assigned a switchable drain valve for deactivation.11. The piston machine of claim 9, wherein the piston units have abypass channel assigned to the corresponding drain valve.
 12. The pistonmachine of claim 9, wherein there are at least three piston units. 13.The piston machine of claim 9, wherein the position machine is at leastone of a radial piston machine, an in-line piston machine, and anin-line piston pump.
 14. The piston machine of claim 9, wherein each ofthe piston units has at least one piston which is axially displaceableinside a cylinder.
 15. The piston machine of claim 9, wherein thedifferently sized output volumes are defined by differently sizedcross-sectional areas of the cylinders and the pistons.
 16. The pistonmachine of claim 9, wherein the differently sized output volumes aredefined by piston strokes of different sizes.